The present disclosure generally relates to a power factor correction circuit and, more particularly, to a control circuit for an active power factor correction circuit.
The power utilization efficiency of electronic devices has become more and more important as the energy shortage problem deteriorates. The traditional AC-to-DC converter is typically realized by using diode rectifiers. Although such structure is simple and low cost, serious non-linear distortion occurs at an input current to greatly increase the low frequency harmonics, thereby decreasing the power factor. The power factor is defined as a ratio of the working power to the apparent power, and is an indicator for measuring the power utilization efficiency. Electronic devices with low power factor not only waste energy, but also generate enormous harmonics to adversely affect the stability to the power system and cause problems to the power generator, thereby seriously affecting the quality of power supply.
A power factor correction (PFC) circuit is employed in many AC-to-DC converters to improve the power factor. In order to avoid a feedback compensation signal from changing with the magnitude of an input voltage, the PFC circuit usually adopts a circuit structure using an input voltage feed-forward control mechanism. Such circuit structure requires a squarer to compute a square value of the input voltage and to generate required control signals by cooperating with a multiplier and a divider.
However, the squarer is not only complex in design, but also occupies considerable circuit area and requires high manufacturing cost and power consumption. Accordingly, the use of the squarer obstructs the PFC circuit to improve the power utilization efficiency and to further reduce the circuit size.